A 1D, finte-difference based model, General Electromigration Model (GEM), was used with modifications for electrochemical kinetics. As expected, the cathdlc hydrogen evolution rate and anodic iron dissolution rates were both found to affect the pH inside the crevice. The model also predicted that formation of iron carbonate, observed extensively in some pipeline failures, occurs under a specitlc combination of iron dissolution rate and hydrogen evolution rate. GEM provides a unique modeling tool because it is flexible enough to test the effects of a variety of
environmental conditions as input parameters and because its
predictions of solid mineral formation in crevices can be tested against field experience. The changes in crevice pH and potential were measured experimentally using microelectrodes. The experimental results at different applied potentials indicated that the experimental results were qualitatively consistent with model predictions.
Keywords: Coating, disbonding, pipelines, cathodic protection